Flow or surface modifiers or control agents or additives are used in the coatings industry to control interfacial tension and surface tension gradients of coating compositions. Lower pollution-type coatings such as waterborne coatings, powder coatings, and, to some extent, high solids coatings utilize flow modifiers to control leveling of the coating film. Typical powder coating compositions contain a flow modifier to enhance their rheology or to control cratering and reduce orange-peel characteristics to provide for smoother, better looking coatings. Common flow modifiers include: acrylics such as poly(2-ethylhexyl acrylate), poly(lauryl acrylate), poly(butyl acrylate), poly(ethylacrylate-2-ethylhexyl acrylate), poly(lauryl methacrylate) and the like (see in this regard U.S. Pat. No. 3,787,340 to Labana et al.). Other useful flow additives include silicon-containing polymers and fluorinated polymers, such as the esters of polyethylene glycol or polypropylene glycol, and fluorinated fatty acids.
Coating compositions used in multilayered coatings for metallic and plastic substrates like those for automotive applications must meet a number of performance requirements which can vary depending on the previous and subsequent coating layers and the application methods and chemistries for the coatings. For example, motor vehicle manufacturers who use powder coating compositions as clearcoats require a degree of compatibility between a variety of powder clearcoats from different sources. Poor compatibility can result in the powder clear coating that is applied subsequently on the manufacturing assembly line having defects from components of the powder clear coating that was previously applied on the line. Such components can act as contaminates in the subsequently applied coating, and contaminants can alter the surface tension gradients in the coating composition resulting in cratering defects.
Also in multilayered coatings on substrates, intercoat adhesion and, in some applications, recoatability can be adversely affected by modifications in the powder coatings to reduce the degree of cratering. For powder coatings applied as primer surfacers or chipguard primers or in basecoat/clearcoat composite coatings that are topcoated with typical finishing coat compositions, the presence of the aforementioned types of flow control agents can adversely affect the intercoat adhesion between the topcoat and the powder primer surfacer.
In addition, powder coatings are often applied as chipcoat primers over uncured, dehydrated electrodeposited coatings (see, for example, U.S. Pat. No. 4,804,581). In such an application, the chipguard primer is only applied to a portion of the electrodeposited coating usually in the areas that are subjected to stone chipping, i.e., rocker panels and wheel wells. The composite coating is co-cured in one step and topcoated with a conventional finishing coat. In applying the chipguard primer to only a portion of the dehydrated, uncured electrodeposited primer, there is an area of overspray where the powder coating composition contacts the electrodeposited primer in areas other than that to be coated. When the chipguard primer contains conventional flow control additives such as those described above, severe cratering of the electrodeposited primer often results. Other applications of powder coatings require recoatability, i.e., good recoat adhesion between the cured powder coating and a subsequent coating layer, so that minor imperfections or minor damage that may occur during shipment and transfer of industrial parts can be corrected. Unfortunately, powder coatings containing the common flow modifiers have been found to have poor crater resistance.
It is an object of the present invention to provide a coating composition with improved compatibility with other similar coating compositions while maintaining good appearance and intercoat adhesion.